MicroRNAs in haematopoietic stem cell transplantation outcome

Abstract

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) is a curative treatment for numerous haematological malignancies. Graft-versus-host disease (GVHD) is the major complication causing mortality and is classified into acute (aGVHD) and chronic. MicroRNAs play a significant role in inflammation and have reported potential as biomarkers of different diseases. This study has investigated the role of microRNAs in allo-HSCT outcomes and had two main aims; (1) identification of microRNAs specific to the aGVHD target organ, skin and (2) an investigation into the role of immune specific miRNAs (miR-146a and miR-155) in peripheral blood. Initially, pathway mining was performed on a list of 18 genes that were shown previously, to have deregulated expression levels with regards to GVHD. The pathway mining identified specific immunological pathways in relation to the genes and potential microRNA targets. Global microRNA profiling was performed on a discovery cohort that identified a signature microRNA list in skin biopsies obtained from patients at the time of cutaneous histopathological aGVHD onset (grades I-III) and healthy volunteers. Twelve microRNAs were selected for further validation and it was shown that miR-34a-5p, miR-34a-3p, miR-503-5p and let-7c-5p were elevated and significantly involved in allo-HSCT outcomes. There was an interaction between miR-34a-3p and miR-503-5p which was significantly diagnostic of aGVHD and let-7c-5p was significantly predictive of disease relapse. MiR-34a-5p protein targets; p53 and c-Myc were then evaluated in the same cohort. MiR-34a-5p expression levels and cells stained positively for p53 were significantly correlated in the epidermis. Preliminary optimization of miR-34a-5p knockdown study was successfully conducted which showed promising results in the reduction of T cell proliferation. The whole blood study showed that miR-146a-5p and its interaction with miR-155-5p was predictive of aGVHD incidence in pre-disease onset (Day+28) samples. Interestingly, the expression levels of miR-146a-5p and miR-155-5p negatively correlated with SPI1 (PU.1). In conclusion, these investigations showed that (1) the microRNAs studied in this investigation may regulate the expression levels of the selected 18 genes, (2) microRNA expression levels in clinical skin biopsies obtained at the time of aGVHD onset could potentially be used as diagnostic biomarkers for aGVHD and as predictive biomarkers for overall survival as well as relapse and (3) miR-146a-5p and miR-155-5p expression levels in whole blood could be used as predictive biomarkers for aGVHD incidence.